1. Field of the Invention
The present invention relates to a pixel drive circuit of a CMOS (Complementary Metal Oxide Semiconductor) type, for example, an image capture device, and a camera system.
2. Description of the Related Art
A CMOS image sensor (image capture device) has a plurality of advantages as follows: a partial reading which is difficult in a CCD (Charge Coupled Device) is possible; the image sensor can be driven by a single power supply; and an analog circuit and a logical circuit using a CMOS process may be mounted together on an identical chip. Because of the advantages, the CMOS image sensor is widely used for a camera, et al.
In such a CMOS image sensor, as shown in FIG. 12, a photodiode 11 as a photoelectric conversion element for converting an incident light into an electric charge is widely used. A pixel circuit 1 transfers the electric charges accumulated in the photodiode 11 via a transfer transistor 12 to a floating diffusion FD. The pixel circuit 1 performs a so-called electric-charge reading operation in which a potential, of the floating diffusion FD, corresponding to an amount of electric charges is amplified in an amplifier transistor 13 and outputted, as a voltage signal (image data), to a signal line LSGN via a selection transistor 14.
Many CMOS image sensors perform electronic shutter process for controlling an exposure time at a time of imaging after the reading operation. In the electronic shutter process, the transfer transistor 12 and a reset transistor 15 are simultaneously switched to ON, the electric charge left in the photodiode 11 is discharged to outside of the pixel circuit 1, thereby adjusting the incident light.
The CMOS image sensor has a processing function called a global shutter in which the electronic shutter processes are performed on all of a plurality of pixel circuits 1. To perform the global shutter, it may be necessary that control signals corresponding to the number of pixels of the image sensor are generated and all the pixel circuits are controlled at once. Such an electronic shutter process or a global shutter process is performed by successively controlling in a row direction a plurality of pixel circuits 1 in which pixel drive circuits are arranged in a matrix shape.
The pixel drive circuit may sometimes be configured to have a memory circuit per each row to impart a degree of freedom of the electronic shutter process to implement a downsizing of a circuit, and causes this storage circuit to store a row which is subject to processing before execution of the electronic shutter process (see Japanese Unexamined Patent Application Publication No. JP 2005-311736, Patent Document 1).